Some medical therapies require that a fluid be infused into a patient's blood circulatory system. Each such infusion may be brief or it may be prolonged depending upon the patient's medical problem. Thus, for example, while one patient may be required to receive an infusion for an hour each week for many months, another patient might require an infusion for a period of one week each month. These regimens might apply, for example, to patients receiving chemotherapy for treatment of cancer. In the most usual procedure, a cannula is inserted through the skin into a vein in the patient's arm or leg. The cannula is then connected by tubing to a supply of the infusate which is administered to the patient in the prescribed amount for the proper length of time. In some cases, however, particularly with older patients, it becomes difficult to repeatedly find accessible venous infusion sites.
Also, when infusing a drug into a patient's venous system, it is sometimes necessary to limit the concentration of the drug because the amount of blood available to mix with the drug is limited by the relatively small diameter of the vein and because blood moves rather slowly through the vein. Therefore, it takes longer for the drug to take effect.
To avoid the aforesaid problems with venous infusion, implantable infusate injection ports have been developed. The injection port includes a chamber within the device and a penetrable self-sealing septum. When the injection port is implanted, that septum is located directly under the skin. A small tube extends from the chamber to the particular infusion site. An example of such a surgical reservoir is disclosed in U.S. Pat. No. 3,310,051. Another such device is marketed by Infusaid Corporation, Sharon, Mass. under the trademark Infuse-A-Port.
Such an appliance, once installed, gives permanent access to a specific internal region of the body and serves as a continuously available conduit placed in the body but once. Thereafter, a hypodermic syringe or drug adminstration cannula need only be placed in fluid communication with the chamber to inject fluids under pressure into the affected interior region of the body. Since the chamber communicates directly with the infusion site, a drug can be administered in higher concentration without unduly adversely affecting the rest of the patient's body. If the chamber communicates with the carotid artery, for example, there is a relatively large volume of relatively fast flowing blood available to mix with the higher-concentration infusate.
When fluid is infused into a patient in the usual way using an injection needle or cannula, the needle can be inserted into a vein, for example, at an angle with respect to the skin surface so that the cannula lies more or less parallel to the vein. In that position, the needle can be taped to the patient's skin. Accordingly, it does not project out from the patient where it could become caught by bedding or clothing and cause discomfort to the patient or, in extreme cases, be pulled from the patient.
However, when a patient is fitted with an implantable infusate injection port, the injection needle must be inserted into the injection port's septum at more or less a right angle to the outlying skin surface. If the infusion is a prolonged one, the needle must remain projecting out of the patient's body in position to be snagged by clothing, bedding, etc. as the patient moves about in the bed or chair. The bending moments applied to the needle are transmitted to the injection port tending to cause tearing of the septum or cocking within the body resulting in patient pain or discomfort. Also, in extreme cases, the needle can be bent or broken by the sideways forces exerted upon it or be pulled out of the injection port causing the drug to be misdelivered to the subcutaneous tissue.
To avoid the aforesaid problems, it is current practice to inject infusate into such implantable injection ports using needles which are prebent more or less at a right angle so that, after insertion of the needle into the port, the needle lies more or less parallel to the patient's skin adjacent the injection site. Thus, it is in a position to be secured to the patient's skin with adhesive tape so that it no longer catches on bedding and clothing. The problem with this procedure, however, is that the distance from the surface of the patient's skin to the injection port varies from patient to patient and, even with a single patient over time as his weight varies. This means that the injection needle must be prebent to suit each patient prior to each injection if it is to penetrate sufficiently into the port and still lie against the skin of the patient. Accordingly, that solution to the needle projection problem is not entirely satisfactory.